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Abstract

Myanmar’s plant diversity is expected to be very high given the wide variety of climates and the diverse vegetation and geographical features of the country. Since the publication of Kress et al.’s plant check-list in 2003, new and unrecorded species have been constantly reported by various botanists, but much of Myanmar’s flora requires more intensive examinations. We conducted joint floristic surveys of several Ywangan areas, including the Panlaung-Pyadalin Cave Wildlife Sanctuary in southern Shan State of Myanmar. The initial identification of seed plant specimens collected from three short floristic expeditions revealed that 23 species were newly recorded species in Myanmar. More than half of these were found to be geographically notable species, which are known to be endemic to neighboring countries such as China (4 spp.), Thailand (6 spp.), and India (2 spp.). A considerable number of these unrecorded species are distributed in the limestone areas of neighboring countries, reflecting the geological characteristics of the survey area. The results of this study reemphasize the need for intensive and continuous research on the flora of Myanmar for a more comprehensive understanding of the distribution patterns of flowering plants in Southeast Asia.

Like all other parts of Myanmar, the flora of Shan State is poorly known. Shan State is a geographical link between China’s Yunnan province and regions of northern Thailand. Therefore, there is a high possibility that species distributed in those regions would occur in the state. In addition, limestone areas commonly appearing in southern Shan State have geological features similar to others in many parts of Thailand (Udchachon et al., 2018), implying the possibility of the occurrence of the Thai endemic species distributed in the limestone zone. Ywangan is a major township in the southern Shan State, adjacent to the Panlaung-Pyadalin Cave Wildlife Sanctuary (PPCWS, see Fig. 1), one of the Myanmar’s 43 protected areas (Beffasti and Galanti, 2011). The climate in this region is characterized by a long, rainy wet season (May to early December) and a relatively short, cool dry (mid-December to February) and hot dry (March to April) seasons. These areas have elevations in the range of 150–1,555 m and exhibit various climatic zones from lowland dry areas to highland rainfall areas. Mixed deciduous forests exist in both the highlands and lowlands, and the average annual rainfall in the area is 1,250–2,000 mm (Beffasti and Galanti, 2011).

With the support of National Institute of Biological Resources (NIBR) of the Republic of Korea and MONREC of Myanmar, we conducted three joint floristic surveys of the Ywangan area from February of 2017 to January of 2018. Initial identification of seed plant specimens collected from the three short floristic expeditions revealed that a considerable number of the identified species are geographically notable species, including many new Myanmar records. Here, we report the list of newly recorded species with their original distribution information and brief taxonomic and/or phytogeographic notes.

Note: This species has the characteristics of a flower of Rungia. However, unlike other species in the genus, which are mostly erect herbs, this species is a vine with a prostrate stem habit. Bracteoles of this species are ovate-lanceolate and are as long as bracts, unlike Rungia chinensis Benth., the most closely allied species (Wu et al., 1994).

Note: This species was first discovered and reported in a limestone area of Thailand. The emergence of this species in this survey area appears to be due to its geological similarity to the type locality in Thailand. The leaf margin (dentation) of the species is unique and easily distinguishable from those of other species in Hydrocotyle (Shimizu et al., 1984).

Note: It is an endemic species distributed in Yunnan (China), and a small number of individuals grow around the forest margins. This species differs from others which closely resemble it, i.e., Pimpinella renifolia H. Wolff, by having cordate-lanceolate or long triangular basal and lowers leaves. This is a very distinguished feature in Pimpinella (Wu et al., 2005).

Note: This species was transferred from Gerbera to Uechtritzia and was recently repositioned to Oreoseris. It is noteworthy that the original distribution of this species and this survey area are approximately 2,300 km away (Xu et al., 2018). Future studies of their disjunctive distribution may also be possible. It is a new genus record in Myanmar.

Note: It was originally described from Thailand, but recently it was reported as a new record of Begonia species in China (Yunnan). Considering the geographical location of the Shan state connecting China and Thailand, it is a species that is likely to be distributed in this survey area (Yang et al., 2015).

Note: It is a species that grows widely in neighboring countries and can be expected to be distributed in Myanmar as well. It is characterized by inflorescence borne at the end of the stem, which is easily distinguished from the species of Carex distributed in Southeast Asia (Nelmes, 1946).

Note: It is an endemic species distributed in southern Thailand. This species has large leaves and dark red or crimsonred flower, which distinguish it well from other species in Didymocarpus (Nangngam and Maxwell, 2013).

Note: Although the distribution area of the species is very wide, ranging from the Philippines to Nepal, it is considered to be a rare species. It is an indicator species of limestone areas and is also found in the limestone areas of many neighboring countries. Currently, several new species are described from Sageretia in limestone areas (Wu et al., 2007b).

Note: It is a Chinese endemic species which grows in hilly areas in the survey area. The species are often shrubby and resemble an oak species. The species is characterized by having an incised-serrate leaf margin and tomentose peduncle and pedicels. The leaf shape is very similar to the closely allied taxon, but the texture is softer (Wu et al., 2007a).

Note: It grows in humid rocky areas and is easily distinguishable from sympatric plant species due to its white fruit on long pedicels. One of the diagnostic characters of the species is the stipules, which is ovate-lanceolate, acuminate or acute at the apex, subscarious. The leaves are glabrous and larger (3.5–9 cm wide) than closely allied species (Yan et al., 2016).

Note: It was first described in Thailand and confirmed to be distributed in China as well. This species is characterized by distinct single mid-vein, pinnate lateral veins and triangular small stipules. The dark green color of the dried leaf is also a distinguishing feature of the species (Wu et al., 1994b). The occurrence of this species can be expected in the survey area, which is connected to two current distribution areas, SW Yunnan and Thailand.

It should be emphasized that a considerable number of newly recorded plant species were collected within the relatively short periods of the expeditions. Considering that most of the examined sites are places easily accessible by car and on foot, the number of new records appears to be relatively high. In addition, many of the newly recorded species are commonly distributed in Yunnan (China) and northern Thailand, filling in the floristic discontinuity between the two areas. The results of this study reemphasize the need for intensive and continuous research on the flora of Myanmar for a more comprehensive understanding of the distribution patterns of flowering plants in Southeast Asia. Furthermore, there are many more species in Myanmar waiting to be described, as much of the country is still untouched and has scarcely been accessed by botanists.

Acknowledgments

This work was supported by grants from the National Institute of Biological Resources (NIBR), the Ministry of Environment (MOE) of the Republic of Korea (NIBR2018 04201). Our gratitude extends to the Ministry of Natural Resources and Environmental Conservation (MONREC) of Myanmar for the continuous guidance and support for this project.

NOTES

Conflict of Interest

The authors declare that there are no conflicts of interests.

Fig. 1.

A map of the surveyed area, showing the distribution of newly recorded Myanmar seed plants. Numbers indicate collected species which appear on the main list of new records. White dotted lines are the boundary of the PPCWS (i.e., the Panlaung-Pyadalin Cave Wildlife Sanctuary).